You?ve all been there: rushing toward the subway stairs, clutching your Times or Savage Detective on your hurried way to work, part of the ever-flowing crowd that is New York City. Ever-flowing, that is, until you reach that person?the man or woman, cellphone to ear?who has decided it?s perfectly acceptable to stop on the subway stairs in order to finish their call, impeding all the rest of us, damming up the crowd like one of those Chinese quake lakes. Citizens: Do not accept this selfishness! Berate these oblivious yappers! Use pointed, intemperate language?sarcasm, if necessary?to assail their breach of the commuters? social contract. For, indeed, upbraiding subway-stair blockers is the best reason to be rude to a stranger.